This application relates generally to containers such as paper or plastic cups used with the dispensing of food products. In order to protect the food within the container from contamination and spillage, it has been common to seal a closure or foil membrane over the top of the cup. Common food products such as milk, juice, jelly and peanuts are packaged with heat sealed foil closures which can be peeled from the top of the cup or container.
In most instances the foil closure is sealed to the top rim of container by the application of heat. The seal between the foil and the container must be leakproof and also provide considerable resistance to being jarred loose by the movement of the product as the containers are transported from place to place.
There have been many approaches to designing an adequate seal between the foil and the top of the container. When the top of the container rim is substantially flat the integrity of the seal is enhanced to a considerable degree. To make a heat seal between a foil-type closure and a rounded top edge on a container requires that a heavy axial loading be applied to the foil. Some containers such as plastic cups collapse under axial loading, therefore, it is imperative that not only a leakproof seal be produced, but also it is important that the container does not collapse under the axial loading required during the sealing operation.